Effective sampling range of a synthetic protein-based attractant for Ceratitis capitata (Diptera: Tephritidae).

Studies were conducted in Honduras to determine effective sampling range of a female-targeted protein-based synthetic attractant for the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Multilure traps were baited with ammonium acetate, putrescine, and trimethylamine lures (three-component attractant) and sampled over eight consecutive weeks. Field design consisted of 38 traps (over 0.5 ha) placed in a combination of standard and high-density grids to facilitate geostatistical analysis, and tests were conducted in coffee (Coffea arabica L.),mango (Mangifera indica L.),and orthanique (Citrus sinensis X Citrus reticulata). Effective sampling range, as determined from the range parameter obtained from experimental variograms that fit a spherical model, was approximately 30 m for flies captured in tests in coffee or mango and approximately 40 m for flies captured in orthanique. For comparison, a release-recapture study was conducted in mango using wild (field-collected) mixed sex C. capitata and an array of 20 baited traps spaced 10-50 m from the release point. Contour analysis was used to document spatial distribution of fly recaptures and to estimate effective sampling range, defined by the area that encompassed 90% of the recaptures. With this approach, effective range of the three-component attractant was estimated to be approximately 28 m, similar to results obtained from variogram analysis. Contour maps indicated that wind direction had a strong influence on sampling range, which was approximately 15 m greater upwind compared with downwind from the release point. Geostatistical analysis of field-captured insects in appropriately designed trapping grids may provide a supplement or alternative to release-recapture studies to estimate sampling ranges for semiochemical-based trapping systems.

Quantifying the impact of chimera MS/MS spectra on peptide identification in large-scale proteomics studies.

A complicating factor for protein identification within complex mixtures by LC/MS/MS is the problem of "chimera" spectra, where two or more precursor ions with similar mass and retention time are co-sequenced by MS/MS. Chimera spectra show reduced scores due to unidentifiable fragment ions derived from contaminating parents. However, the extent of chimeras in LC/MS/MS data sets and their impact on protein identification workflows are incompletely understood. We report ChimeraCounter, a software program which detects chimeras in data sets collected on an Orbitrap/LTQ instrument. Evaluation of synthetic chimeras created from pairs of well-defined peptide MS/MS spectra reveal that chimeras reduce database search scores most significantly when contaminating fragment ion intensities exceed 20% of the targeted fragment ion intensities. In large-scale data sets, the identification rate for chimera MS/MS is 2-fold lower compared to nonchimera spectra. Importantly, this occurs in a manner which depends not on absolute precursor ion intensity, but on intensity relative to the median precursor intensity distribution. We further show that chimeras reduce the number of accepted peptide identifications by increasing false negatives while showing little increase in false positives. The results provide a framework for identifying chimeras and characterizing their contribution to the poorly understood false negative class of MS/MS.